The disclosure relates generally to energy generation systems, and more particularly, to integrated solar energy generation, energy storage and electric vehicle charging systems.
In the United States only about one percent of homes currently are equipped with solar panels, and only about 1 percent of these homes are storing the generated electric power in batteries. A basic solar system consists of an array of panels oriented to receive direct sunlight, one or more inverters to convert the DC power from the array of solar panels to AC, and a physical interface to the customer's existing electrical system. Inverters come in two main form factors—micro-inverters, which are small inverters connected directly to one or more panels at the point of the array, and string inverters which receive the aggregated serialized output of several solar panels. An average solar powered U.S. home may have a 5 to 6 kW array requiring a 5 to 6 kW PV string inverter. This size system typically generates about 1,200 to 1,800 kWh of electricity per month depending on the geographical location and time of the year. Since a 3-bedroom home typically utilizes about 800 to 1,000 kWh per month, customers often generate excess energy, in particular during the summer. That excess electric energy can be fed to the utility grid. The process of back feeding excess power to the grid is known as net energy metering (NEM) or simply net metering. Existing net energy metering (NEM) incentives for PV inverters are about 8 to 12 cents/kWh. In other words, customers are compensated or credited by the utility in that amount for each kWh of power supplied to the grid. This excess energy can be used to offset the customers' consumption during times of year when solar power product is lower (e.g., during winter). Although popular with solar customers, net metering is increasingly under attack from entrenched utilities who want to compensate customers at lower rates, add monthly self-generation charges, and in some cases penalize customers for back feeding any power to the grid. This change in the regulatory landscape has made widespread deployment of storage critical to the continued growth of solar. By storing power generated during the day, customers can then utilize that power at night, reducing their reliance on grid power while maximizing the value of their solar system without needing NEM.
Electric vehicles (EVs) have also gained popularity recently due to great advances in lithium-ion battery technology that extends the range of EVs above 200 miles, drastic reduction in costs year over year, exciting new models of electric cars that rival or surpass the performance of comparable gasoline powered cars, and increased interest in supporting clean energy. These factors have caused the automotive industry to begin to shift focus to develop more electric vehicles (EVs). Products such as the Chevy Volt, Nissan Leaf, and Tesla Model S are currently very popular in the market. The energy capacity of the batteries used in these exemplary EVs varies widely. For example, the capacity of Chevy Volt's battery is 25 kWh, that of Nissan leaf is 35 kWh, and that of Tesla Model S ranges from 60 to 100 kWh. On average, every kWh of energy can provide about 3 to 5 miles of driving range to these EVs.
EV drivers have to charge their vehicles regularly, either at home, at work, or in one of many publically available EV charging stations (e.g., shopping centers, privately owned charging stations, or in the case of Tesla, one of the proprietary stations in their network of Superchargers). The number of miles of range obtained per unit of charging time will depend on how much current is conducted by the charger. Today's chargers for EVs can be categorized into three types: slow chargers that supply about 5 kW, medium chargers that supply about 15 to 30 kW, and fast chargers that supply about 100 to 135 kW.
The proliferation of EVs will increased the demand for electricity and should have a positive effect on the adoption of solar. However, the generation of solar energy has a diurnal cycle, and is therefore not be available in the nighttime when EVs often need to be charged. Therefore, storage of electrical energy for continuous electricity provision at any time of the day and advanced electric charging systems also need to be developed along with the increased deployment of EVs. Current solar energy generation and storage systems provide no provisions for direct charging of EVs. Rather EVs are charged by the power provided directly from the utility grid, usually via a special charger customers can purchase from the automaker or a third party that plugs into a conventional 120V or 240V wall outlet. Thus, there is a need for an integrated solar energy generation and storage system with efficient and cost effective EV charging capability.